This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. At its present level of resolution, ~0.7x0.75x0.75[unreadable]m, the ACERT Ku-band pulse ESR microscope utilizes peak gradient coil drive voltages of up to 425 volts. For observation of biological ESRM signals, we desire a significantly shorter gradient pulse interval, implying higher voltages and smaller values of driver network energy storage capacitance. Our goals are generation of peak coil drive voltages up to 600 volts, minimum, and pulse widths of 800ns or less at peak gradients approaching 100 T/m. The strategy for accomplishing significantly reduced pulse widths is to upgrade the gradient driver subsystem by installation of 800 volt MOSFET output devices in place of the prior 600 volt devices, and to replace the existing preregulator system that is employed to precharge the driver channel high-voltage capacitors with a substantially upgraded version. Modifications of the gradient driver subsystem to achieve higher output voltage capability have already been made. However, the preregulator driving it is capable of only 450 volts, although ca 11 amperes peak current output. We will replace the preregulator within a few weeks with a MKII version providing two channels of at least 800 volt, 10 amperes capability. With this combined gradient driver system, we anticipate utilizing spin probes with shorter T2, e.g. nitroxides, that are appropriate for biological imaging.